Some metal components, such as turbine components, operate under extreme operating conditions. The turbine can be a gas turbine, a hydroelectric turbine, a steam turbine, or the like. The foregoing extreme operating conditions include elevated temperatures, elevated pressures, corrosive environments, friction, erosion, or the like, or a combination thereof.
The metal components can be subjected to two or more of the foregoing extreme operating conditions in combination, such as, corrosion and erosion. For example, a hydroelectric turbine component can be subjected to erosion by impingement of silt (sand in the water) and particles contained therein (e.g., SiO2, Al2O3, Fe2O3, MgO, CaO, clays, volcanic ash, and the like) that are carried by moving bodies of water. A steam turbine component can be subjected to erosion due to water droplets. During the operation of an industrial gas turbine or steam turbine, water droplets tend to form or are deliberately introduced, as in the case of the gas turbine. The droplets can deposit on stationary components where they coalesce into films or rivulets and slowly move to the trailing edge of the component. The films and/or rivulets are then removed by the steam flow in the form of large drops. These large drops impact certain components at an elevated velocity. The impact of water drops generates an impulsive contact pressure on the component surface causing progressive loss of component material, i.e., erosion.
In addition to erosion, the above exemplified hydroelectric turbine component, industrial gas turbine component, and steam turbine component can additionally be subjected to corrosion. For example, water, steam, metal salts such as alkaline sulfate, sulfites, chlorides, carbonates, oxides, and other salts resulting from ingested dirt, fly ash, volcanic ash, concrete dust, sand, sea salt, or the like, are a source of corrosion. Corrosion causes pitting and/or loss of the metal components, which can lead to failure or premature removal and replacement of the components.
The metal components are generally provided with separate coatings that impart various characteristics, such as corrosion resistance, heat resistance, oxidation resistance, wear resistance, erosion resistance, or the like. However, there is a lack of coatings that are singly effective at addressing a combination of two or more of the foregoing extreme operating conditions, such as a combination of corrosion and erosion.
Therefore, a coating that is effective at protecting a metal component, such as a turbine component, against the simultaneous negative effects of corrosion and erosion would be advantageous.